A conventional conveyor is known that includes a plurality of rollers arranged to convey objects to be conveyed, a plurality of sprockets each of which is provided so as to be coaxial with the roller and rotate together therewith, an endless chain wound onto these sprockets, another chain wound onto some of the sprockets and onto a driving sprocket of a driving source in order to provide a driving force, and a tension adjusting mechanism that automatically adjusts the tension of the chains.
In this apparatus, if an elongation occurs in the chains wound onto the sprockets, for example, because of a time-dependent change caused by a conveying operation, the chain wound onto the driving sprocket is adjusted to automatically absorb the elongation by means of the tension adjusting mechanism. On the other hand, there is a fear that the chain wound onto the other sprockets that rotate together with the rollers will be disengaged from the sprockets when looseness is caused in proportion to the elongation. Therefore, to remove this looseness, the conveyor is required to be regularly stopped and be adjusted (for example, see Japanese Published Unexamined Utility Model Application No. H5-82926).
However, the operation of the apparatus must be stopped for the adjusting work during which productivity is lowered, and the adjusting work is troublesome. On the other hand, if the tension adjusting mechanism is provided, the adjusting work becomes unnecessary, but the tension given to the chain will cause an increase in a driving load. Additionally, the tension adjusting mechanism is complex, and a space to dispose the mechanism is needed, and, furthermore, the tension adjusting mechanism leads to a rise in the cost of the apparatus.
The present invention has been made in consideration of the foregoing circumstances. It is therefore an object of the present invention to provide a chain-driving mechanism that has a simple structure, that is low in cost, that is not required to adjust an elongation even if such an elongation occurs in a chain, that can prevent a chain from slipping off from sprockets or from being positionally inaccurately engaged therewith, and that can reliably transmit a driving force, and to provide a conveyor apparatus using this chain drive mechanism.